1. Technical Field
The present invention relates to a piezoelectric vibrating element that includes a main vibrating unit and an outer frame unit surrounding the main vibrating unit integrally on an identical piezoelectric substrate, and a piezoelectric vibrator.
2. Related Art
In these years, as electronic apparatuses are becoming smaller and smaller in size, piezoelectric vibrators used for such electronic apparatuses and piezoelectric vibrating elements used for such piezoelectric vibrators are also required to be reduced in size and in thickness. A piezoelectric vibrating element 500, for example, such as shown in FIG. 11 is proposed in order to reduce, in size and in thickness, piezoelectric vibrators and piezoelectric vibrating elements used for such piezoelectric vibrators. FIG. 11 shows, as an example of a conventional piezoelectric vibrating element, an AT cut vibrating element that uses a quartz substrate. FIG. 11A is a plan view, while FIG. 11B is a front sectional view. As shown in FIGS. 11A and 11B, the piezoelectric vibrating element 500 is composed of a main vibrating unit 502 formed on the center part of a quartz substrate (quartz wafer) 501, an outer frame unit 503 and a connecting unit 504. The main vibrating unit 502, the outer shape of which is formed by a through hole 505 placed around its periphery, is connected integrally to the outer frame unit 503 with two connecting units 504, which are areas where the through hole 505 is not formed. The connecting unit 504, the width of which is around 200 μm, is formed in a manner that its top and bottom faces 508 and 509 are placed closer to the center of the thickness direction than the top and bottom faces 506a and 506b of the main vibrating unit 502 and the top and bottom faces 507a and 507b of the outer frame unit 503. Therefore, the top and bottom faces 508 and 509 of the connecting units 504 are connected to the top and bottom faces 506a and 506b of the main vibrating unit 502 and to the top and bottom faces 507a and 507b of the outer frame unit 503, respectively with a certain level difference. The outer frame unit 503 is formed approximately in a manner of surrounding the periphery of the main vibrating unit 502, as is proposed, for example, in JP-A-7-212171. Exciting electrodes 510a and 510b are formed on the top and bottom faces 506a and 506b of the main vibrating unit 502. In connection with the exciting electrodes 510a and 510b, connecting electrodes 511a and 511b are formed, passing through the connecting units 504 to reach the top and bottom faces 507a and 507b of the outer frame unit 503. The connecting electrodes 511a and 511b are formed with a metal thin film such as gold or silver by a chemical etching method using a photoresist as a mask.
However, the top and bottom faces 508 and 509 of the connecting units 504 are formed so as to respectively have a certain level difference, with respect to the top and bottom faces 506a and 506b of the main vibrating unit 502, and with respect to the top and bottom faces 507a and 507b of the outer frame unit 503, as mentioned above. Thus, corner parts (ridge line parts) 512a and 512b are formed that are made with the side surfaces of the part corresponding to the level difference and the top and bottom faces 506a and 506b of the main vibrating unit 502, as well as the top and bottom faces 507a and 507b of the outer frame unit 503. There is a case where the angle D on the corner parts 512a and 512b becomes smaller than 90 degrees in the course of forming the outline of the piezoelectric vibrating element 500. In such a case that the angle D on the corner parts 512a and 512b becomes smaller than 90 degrees, a photoresist for forming the connecting electrodes 511a and 511b and the like may sometimes not be formed on the corner parts 512a and 512b. 
This phenomenon may be attributed to the following causes. (1) The photoresist is drawn bilaterally at the corner parts 512a and 512b due to the surface tension of the photoresist. (2) The photoresist is usually applied using a device called a spin coater. This device, using the centrifugal force created by spinning the quartz substrate 501, applies the photoresist dropped on the center part of the quartz substrate 501 to all over the quartz substrate 501. At this timing, in the case where any above-mentioned angle D is smaller than 90 degrees on the surface of the quartz substrate 501, resulting in some areas on which the photoresist is not applied since clearances are too small for the photoresist to enter them.
If chemical etching is carried out in such a situation for forming the connecting electrodes 511a and 511b and the like, the connecting electrodes 511a and 511b are exposed with the etching solution, that correspond to the corner parts 512a and 512b which are not masked with the photoresist. Thus, a problem in that the connecting electrodes 511a and 511b are blown out, so-called an electrode disconnection, occurs at the corner parts.